1. Field of the Invention
The present invention relates to a magneto-resistance effect element and a thin-film magnetic head.
2. Description of the Related Art
Magnetic disk drives employ a thin-film magnetic head having a magneto-resistance effect element (MR element) for reading magnetic signals. In recent years, efforts have been made to design magnetic disk drives for higher recording densities, and accordingly there are growing demands for thin-film magnetic heads, particularly magneto-resistance effect elements, which satisfy higher-sensitivity and higher-output requirements.
A CIP-GMR (Current in Plane—Giant Magnetoresistance) element which is a giant magneto-resistance effect element having a nonmagnetic layer between ferromagnetic layers and passing a sensing current in parallel to a layer surface, has been conventionally developed as a reproducing element in a thin-film magnetic head. On the other hand, a magnetic head that uses a TMR (Tunnel Magneto-resistance) element which has an insulation layer instead of the nonmagnetic layer as an intermediate layer and which passes a sensing current perpendicular to a layer surface, has also been developed in order to achieve higher densification. Furthermore, a magnetic head that uses a CPP (Current Perpendicular to Plane)-GMR element which is a GMR element having a nonmagnetic layer as the intermediate layer and passing a sensing current perpendicular to the layer surface similar to the TMR element, has also been developed. CPP-GMR element has an advantage of having low resistance in comparison with the TMR element and having higher output in a narrower track width than the CIP-GMR element.
An ordinary GMR element is in the cylindrical shape of a desired size, and has a structure interposing a non-magnetic spacer layer between a pinned layer which is a ferromagnetic layer in which the magnetization direction is fixed a and a free layer which is a ferromagnetic layer in which the magnetization direction varies according to an external magnetic field. Such a GMR element is also referred to as a spin valve film (SV film). The upper and lower ends of the GMR element are provided with a cap layer and a buffer layer, respectively. The cap layer, the GMR element, and the buffer layer are interposed between the upper shield layer and the lower shield layer. In the case of the CPP-GMR element, the upper shield layer and the lower shield layer function as an electrode, respectively, and a sense current flows in a direction orthogonal to the layer surface.
The spacer layer of a conventional CPP-GMR element has been most commonly comprised of Cu that is about 3.0 nm in thickness. However, in the CPP-GMR element having a spacer layer comprising Cu, since Cu has a low resistance, the sheet resistance (RA value) is low, and, for example, it is 0.07 Ω·μm2, and the MR ratio is also low, and it is below about 4%. In this CPP-GMR element, to obtain a sufficient output voltage, it has been necessary to operate the element at a high current density. When the element is operated at the high current density, an electro-migration phenomenon occurs in which a metallic atom colliding with an electron migrates, and there is a fear that the magneto-resistance effect element will be destroyed by the migration of the atom and its life span becomes extremely short. Further, when the element is operated at the high current density, an output noise caused by a spin transfer torque occurs, and a practical problem arises.
To increase the RA value of the CPP-GMR element, a confined-current-path type magneto-resistance effect element has been proposed, in which a non-current portion is provided inside the spacer layer and the current is allowed to flow in a direction vertical to the layer surface by passing through only certain portions inside the spacer layer. In the confined-current-path type magneto-resistance effect element, the resistance of the spacer layer can be substantially high, thereby the RA value can be high. However, such a confined-current-path type magneto-resistance effect element has been difficult to manufacture, and it was extremely difficult to form the element at a high dimensional accuracy so as to be able to obtain desired performance.
Structures that have been proposed to increase the RA value of a CPP-GMR element without the confined-current-path technique include a structure wherein the spacer layer is made of three layers, i.e., a first interface layer, an electrically conductive layer, and a second interface layer, and a structure wherein a resistance adjusting layer is provided adjacent to the spacer layer. These proposed structures which have a substantial multilayer structure as the spacer layer have their MR ratio higher to some degree than a spacer layer in the form of a single Cu layer. However, though many materials may be used as the materials that makes up each layer of the spacer layer, specific materials that are best for increasing the MR ratio have not been proposed in the art.
A so-called synthetic pinned layer, which does not have a single-layer structure made of a ferromagnetic material, but has a multilayer structure including a nonmagnetic metal layer interposed between a plurality of ferromagnetic layers, has been employed as the pinned layer. The synthetic pinned layer gives strong exchange coupling between the two ferromagnetic layers to effectively increase the exchange coupling force from the antiferromagnetic layer.
Japanese Patent Laid-Open No. 2005-19484 discloses a pinned layer that has a five-layer structure comprising a first ferromagnetic layer, an anti-parallel coupling layer, a second ferromagnetic layer, a high polarizability layer, and an intermediate ferromagnetic fixed layer. Specifically, the first and second ferromagnetic layers and the intermediate ferromagnetic fixed layer are made of CoFe, the anti-parallel coupling layer is made of Ru, and the high polarizability layer is made of a Heusler alloy such as CoMnGe.
Japanese Patent Laid-Open No. 2003-218428 discloses a pinned layer that has a five-layer structure comprising a first magnetic layer comprising three magnetic layers, a nonmagnetic intermediate layer, and a second magnetic layer. Specifically, the second magnetic layer is made of CoFe, the nonmagnetic intermediate layer is made of Ru, the central layer of the first magnetic layer is made of a half metal such as a Heusler alloy, and the upper and lower layers of the first magnetic layer are made of CoFe.
FIGS. 11A through 13 of Japanese Patent Laid-Open No. 2001-237471 disclose a pinned layer that has a five-layer structure comprising a first metal magnetic layer, a nonmagnetic layer, a second metal magnetic layer, an oxide magnetic layer, and a third magnetic layer. Specifically, the first through third metal magnetic layers are made of CoFe, the nonmagnetic layer is made of Ru, and the oxide magnetic layer is made of Co—Fe—O.